BEIJING -- The death toll from a Tibet tour bus's plunge into a river has risen by two to 14, state media reported Saturday.

Twelve people were killed on the spot in the accident Friday about 90 kilometers (55 miles) west of the regional capital, Lhasa, the official Xinhua News Agency reported. Thirteen people were injured, and two were missing.

The cause of the accident was under investigation. The highway, in rugged mountains along the Yarlung Zangbo River, was renovated last year and is in good condition, Xinhua said.

When the 35-seat tour bus crashed it had 29 people aboard: 27 Chinese tourists, a tour guide and a driver, the agency reported.

The tour group had been traveling to the western city of Xigaze from Lhasa when the accident occurred.

China's roads are among the world's most dangerous, with many accidents caused by reckless driving, poor road conditions and overloading of vehicles.